Abstract
Purpose :
To investigate the usefulness of an in vitro test system as a potential screening tool for predicting the propensity of Intraocular Lens (IOL) materials to calcify in vivo.
Methods :
Calcification of IOLs was simulated in vitro using a batch reactor in which lens materials were exposed to solutions simulating aqueous humor (AH). Measurements of the kinetics of formation of hydroxyapatite, Ca5(PO4)3OH, (HAP) at sustained supersaturation, were used to compare the relative tendency of IOL towards calcification. Lenses were also surgically implanted into rabbit eyes (n=140) and followed for time periods ranging from 3 weeks to 6 months. The lenses were retrieved and evaluated for evidence of IOL calcification using scanning electron microscopy with energy dispersive X-ray spectroscopy. The three test lenses were all made from hydrophobic material and the one control lens was a hydrophilic material.
Results :
The IOLs tested showed a trend towards calcification correlating with contact angle values. The hydrophobic IOLs in contact with calcium phosphate solutions of the same range of relative supersaturation with respect to HAP even though they showed minimal mineralization. HAP growth rates of three sets of Hydrophobic IOLs were compared with the respective for one hydrophilic IOL (water content 26%). Significant differences in the HAP growth rates were found at the 0.05 level with p=0.00461. Despite the fact the supersaturation was comparable to the corresponding AH, the in vitro tests may show mineralization even in cases in which there is no mineralization in vivo. The obvious reason is that the presence of macromolecules (e.g. albumin) and/or smaller ionized species (ascorbic acid) may retard the development and the crystal growth. No IOL calcification was observed in vivo in any of the IOL implanted in rabbit eyes.
Conclusions :
The in vitro and in vivo studies have demonstrated comparable results. The correlation from bench testing to clinical use provides a coherent set of data. The use of the in vitro model as a screening tool has several benefits, including duration, cost, and animal welfare. The in vitro system developed for testing mineralization both in batch and in reactors simulating eye chamber, allows for rapid screening of intraocular lens materials within a week prior to initiating costly animal studies which take months to complete.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.